The present invention relates to hydrodynamic bearings. In such bearings, a stationary bearing pad supports a rotating object such as a shaft via a pressurized fluid such as oil, air or water. Hydrodynamic bearings take advantage of the fact that when the rotating object moves, it does not slide along the top of the fluid. Instead, the fluid in contact with the rotating object adheres tightly to the rotating object. Motion is thus accompanied by slip or shear between the fluid particles through the entire height of the fluid film. Thus, if the rotating object and the contacting layer of fluid move at a velocity that is known, the velocity at intermediate heights of the fluid thickness decreases at a known rate until the fluid in contact with the stationary bearing pad adheres to the bearing pad and is motionless. The load resulting from the bearing pads support of the rotating object causes the bearing pad to deflect at a small angle to the rotating member. Fluid moving with the shaft is drawn into the wedge-shaped opening. Sufficient pressure is generated in the fluid film to support the load. Both thrust bearings and conventional hydrodynamic journal bearings operate on this principle. Both thrust bearings and radial or journal bearings normally are characterized by shaft supporting pads spaced about an axis. The axis about which the pads are spaced generally corresponds to the longitudinal axis of the shaft to be supported for both thrust and journal bearings. This axis may be termed the major axis.
U.S. Pat. No. 3,107,955 to Trumpler discloses one example of a bearing having beam mounted bearing pads that displaces with a pivoting or swing-type motion about a center located in front of the pad surface. This bearing, like many prior art bearings, is based only on a two dimensional model of pad deflection. Consequently, optimum wedge formation is not achieved.
In the Hall patent, U.S. Pat. No. 2,137,487, there is shown a hydrodynamic moveable pad bearing that develops its hydrodynamic wedge by sliding of its pad along spherical surfaces. In many cases the pad sticks and the corresponding wedge cannot be developed. In the Greene Patent, U.S. Pat. No. 3,930,691, the rocking is provided by elastomers that are subject to contamination and deterioration.
U.S. Pat. No. 4,099,799 to Etsion discloses a non-unitary cantilever mounted resilient pad gas bearing. The disclosed bearing employs a pad mounted on a rectangular cantilever beam to produce a lubricating wedge between the pad face and the rotating shaft. Both thrust bearings and radial or journal bearings are disclosed.
There is shown in the Ide patent, U.S. Pat. No. 4,496,251 a pad that deflects with web-like ligaments so that a wedge shaped film of lubricant is formed between the relatively moving parts.
U.S. Pat. No. 4,515,486 discloses hydrodynamic thrust and journal bearings comprising several bearing pads, each having a face member and a support member that are separated and bonded together by an elastomeric material.
U.S. Pat. No. 4,526,482 discloses hydrodynamic bearings that are primarily intended for process lubricated applications, i.e., the bearing is designed to work in a fluid. The hydrodynamic bearings are formed with a central section of the load carrying surface that is more compliant than the remainder of the bearings such that they will deflect under load and form a pressure pocket of fluid to carry high loads.
It has also been noted, in Ide U.S. Pat. No. 4,676,668, that bearing pads may be spaced from the support member by at least one leg which provides flexibility in three directions. To provide flexibility in the plane of motion, the legs are angled inward to form a conical shape with the apex of the cone or point of intersection in front of the pad surface. Each leg has a section modulus that is relatively small in the direction of desired motion to permit compensation for misalignments. These teachings are applicable to both journal and thrust bearings. While the disclosure of this patent represents a significant advance in the art, it has some shortcomings. One such shortcoming is the rigidity of the support structure and bearing pad which inhibits deformation of the pad surface. Further, the bearing construction is not unitary.
The last two patents are of particular interest because they demonstrate that despite the inherent and significant differences between thrust and journal bearings, there is some conceptual similarity between hydrodynamic journal bearings and hydrodynamic thrust bearings.
This application is directed to low profile hydrodynamic thrust bearings. When the hydrodynamic wedge in such bearings is optimized, the load on each of the circumferentially spaced bearings is substantially equal.
Presently, the most widely used hydrodynamic thrust bearing is the so-called Kingsbury shoe-type bearing. The shoe-type Kingsbury bearing is characterized by a complex structure that includes pivoted shoes, a thrust collar which rotates with the shaft and applies load to the shoes, a base ring for supporting the shoes, a housing or mounting which contains and supports the internal bearing elements, a lubricating system and a cooling system. Because of this complex structure, Kingsbury shoe-type bearings are typically extraordinarily expensive.
An alternative to the complex Kingsbury shoe-type bearing is the unitary pedestal bearings shown in FIGS. 19-20. This bearing has been employed in, among other things, deep well pumps. This relatively simple structure is typically formed by sand casting or another crude manufacturing technique because previously, the specific dimensions have not been deemed important. As shown in FIGS. 19 and 20, the bearing is structurally characterized by a flat base 36PA having a thick inner circumferential projection 38PA, a plurality of rigid pedestals 34PA extending transversely from the base and a thrust pad 32PA centered on each rigid pedestal.
FIG. 20(A) illustrates schematically the deflection of the bearing of FIGS. 19-20 in response to movement of the opposing thrust runner in the direction of arrow L. In FIG. 20(A), the deflected position (greatly exaggerated) is illustrated in solid lines and the non-deflected position is illustrated in phantom. The curve PD in FIG. 20(A) illustrates the pressure distribution across the face of the pad. Under load, the thrust pads deflect around the rigid pedestals in an umbrella-like fashion as shown in FIG. 20(A). By virtue of this umbrella-like deflection, only a partial hydrodynamic wedge is formed. Consequently, there is an uneven distribution of pressure across the face of the pad as illustrated in FIG. 20(A). Thus, the bearing has proportionately less hydrodynamic advantage compared to a bearing in which a hydrodynamic wedge is formed across the entire thrust pad face. Moreover, the rigidity of the pedestals and flat inflexible base prevent the deflections necessary to optimize wedge formation. This may explain why bearings of the type shown in FIGS. 19-20, while far less expensive than Kingsbury bearings, have proved less efficient and capable and consequently less successful than the shoe-type bearings.
Additional background relating to this application may be gleaned by reviewing applicant's recently issued patents including U.S. Pat. No. 5,255,984 which shows a variable characteristic thrust bearing. The bearing includes separately formed pads of various shapes and materials that are supported in a carrier. The carrier is constructed such that the pads may be located in separate openings to vary the support characteristics. U.S. Pat. No. 5,222,815 shows a variety of unitary bearings, including journal, thrust and combined radial and thrust bearings of the type having beam mounted bearing pads. The pads and support structure may be integrally formed as a single piece. Similarly, U.S. Pat. No. 5,137,373 discloses thrust, radial and combined radial/thrust bearings in which the pads and support structure are integrally formed as a single piece.
U.S. Pat. No. 5,125,754 discloses thrust and journal bearings having a modular construction. In general, the bearings disclosed therein include separate pads or pad portions that are mounted in a separate carrier. Various pad and carrier configurations are disclosed.
U.S. Pat. No. 5,102,236 discloses hydrodynamic thrust and radial bearings that each have a continuous beam mounted shaft support surface.